Technical Field
The present invention relates to a curling detection device, an image forming apparatus, a curling detection method, an image adjustment method, a non-transitory recording medium storing a curling detection program, and a non-transitory recording medium storing an image adjustment program.
Background Art
Tandem-type electrophotographic color image forming apparatuses, in which image forming units that form images in four colors, black, cyan, magenta, and yellow are disposed along an endless conveyance belt or an intermediate transfer belt that conveys a recording medium (hereinafter referred to as a “sheet”) is known in the art.
In the image forming units of each color, a writing unit irradiates a photoconductor with a laser beam modulated by image data and an electrostatic latent image is formed on the photoconductor. Toner images in each color are formed by supplying toner of each color to the photoconductor on which the electrostatic latent image is formed, and a color image is formed by transferring the toner image on the photoconductor for each color on the sheet conveyed on the conveyance belt or the intermediate transfer belt. In case of transferring an image on the intermediate transfer belt, the color image forming apparatus transfers the color image on the intermediate transfer belt to the sheet fed from a paper feeding unit using a transfer roller.
As described above, in the color image forming apparatus that includes multiple image forming units, unlike a single-drum color image forming apparatus that has only one photoconductor and forms a color image, the color image is formed by superimposing toner images in different colors sequentially on the same sheet or the same surface of the intermediate transfer belt using each of the image forming units. Therefore, if the intervals between the images formed by each of the image forming units is shifted or where those images are imposed on a position on the sheet or the intermediate transfer belt where the image is transferred by each of the image forming units is shifted, image quality deteriorates.
To cope with this issue, a color image forming apparatus that forms predetermined color toner patterns in each color on the sheet, the conveyance belt, or the transfer belt and calculates displacements in the main scanning direction and the sub-scanning direction, magnification shift, skew, and curve by detecting those color toner patterns (especially the interval between the toner patterns) with an optical sensor and reduces color shift by performing feedback correction is known in the art. This so-called color shift correction process is performed when the image forming apparatus is turned on, when environmental conditions such as temperature change, or when the number of printed sheets reaches or exceeds a predetermined threshold. As a result, the amount of color shift always becomes equal to or smaller than a predetermined range.
However, in case of forming the color toner patterns on the intermediate transfer belt, it is impossible to correct color shift precisely if a color order of the color toner patterns gets reversed due to deterioration of the intermediate transfer belt or changes in the environment such as temperature. In some cases, curling of the conveyance roller itself that tensions the conveyance belt or the intermediate transfer belt changes the color order of the color toner patterns described above.
Accordingly, in an image forming apparatus constructed of an image bearer that bears toner images such as a position adjustment pattern and a density adjustment pattern for color matching formed by a toner image forming unit, a rotatable endless belt tensioned by at least two rollers, a transferring unit that transfers the toner image on the image bearer to the surface of the endless belt, and a detecting unit that detects the position adjustment pattern and/or the density adjustment pattern transferred on the surface of the endless belt by the transferring unit, the detecting unit detects curling by rotating the endless belt at least once, and, if curling is detected, the position adjustment pattern and/or the density adjustment pattern is formed so that they are not superimposed on the curled part, and the endless belt is stopped so that the curling is positioned at the roller that caused the curling.
That is, in the technology described above, the endless belt on which the toner image is transferred is rotated at least once, the detecting unit detects curling of the endless belt, and the position adjustment pattern and the density adjustment pattern is formed so that they are not superimposed on the curling and color shift correction is performed.